hi bubbly, sorry to hear that. my deepest sympathy for you and your kids. how old are them? if they're old enough you can talk to them, but if they're too young to understand, just wait until they're ready or ask.
I think first U shud talk to ur husband and then both of you decide when to tell them. and it's better that they know from U both. anyway they come to know about it by themselves slowly. I think if they r in boarding they must have good age